1. Transaxial PET without attenuation correction.
Monday Case of the Day
Physics
Paul E. Kinahan, PhD
Imaging Research Laboratory, Department of Radiology, University of Washington, Seattle
History:
49-year-old male with suspicion of cancer. FDG PET images show abnormally increased FDG uptake below carina and a high-density object in the same region on the noncontrast CT (arrow).
Challenge: What are the potential causes of the FDG abnormality?
Transaxial CT.
Transaxial PET without attenuation correction.
Transaxial PET.
(Images courtesy of Todd Blodgett, MD, UPMC.)

2. Transaxial PET without attenuation correction.
Monday Case of the Day: Physics Paul E. Kinahan, PhD Imaging Research Laboratory, Department of Radiology, University of Washington, Seattle
Answer
On the PET image without attenuation correction (which is not quantitatively accurate but can be a useful secondary check), the region of abnormal uptake is not evident.
The abnormal uptake on PET is thus an artifact, likely due to an unusual calcium deposit below the carina (seen on CT).
PET/CT scanners use the CT images for attenuation correction of the PET data, but this is an approximate correction that does not work well for high-Z materials (eg, contrast agents or implants).
If there is a concern about artifacts, the recommended procedure is to check the PET image without attenuation correction (Kinahan et al. Semin Nucl Med 2003;33: ).
(Images courtesy of Todd Blodgett, MD, UPMC.)
Transaxial CT.
Transaxial PET without attenuation correction.
Transaxial PET.